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Long Length Reactive Evaporation of Seed Layers for YBCO Coated Conductors

IP.com Disclosure Number: IPCOM000035586D
Publication Date: 2005-Jan-25
Document File: 3 page(s) / 612K

Publishing Venue

The IP.com Prior Art Database

Abstract

The purpose of this invention is to provide a reproducible and production scaleable technique to deposit a seed layer for an HTS YBCO conductor structure using reactive electron beam deposition and a ex situ post heat treatment. There are several critical process conditions that must be met to obtain an epitaxial seed layer with larger grain size, stable stoichiometry and high quality texture on a Nickel or Nickel alloy textured substrate. First, the substrate itself must be free of surface oxides. Secondly, the Nickel tape must be at high temperature at deposition atmosphere prior to deposition. Finally to improve the texture and stability of seed layers after vacuum deposition, the seed layer should be post heat treated in the proper atmosphere and temperature. The main features of the invention are a method for heating the tape during the deposition, the methodology for evaporating the seed, the method of introducing and constraining the reactive gas in the chamber near the substrate tape, and the ex situ heat treatment of seed layer after deposition.

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Long Length Reactive Evaporation of Seed Layers for YBCO Coated Conductors

General Purpose of Invention

The purpose of this invention is to provide a reproducible and production scaleable technique to deposit a seed layer for an HTS YBCO conductor structure using reactive electron beam deposition and a ex situ post heat treatment. There are several critical process conditions that must be met to obtain an epitaxial seed layer with larger grain size, stable stoichiometry and high quality texture on a Nickel or Nickel alloy textured substrate. First, the substrate itself must be free of surface oxides. Secondly, the Nickel tape must be at high temperature at deposition atmosphere prior to deposition. Finally to improve the texture and stability of seed layers after vacuum deposition, the seed layer should be post heat treated in the proper atmosphere and temperature. The main features of the invention are a method for heating the tape during the deposition, the methodology for evaporating the seed, the method of introducing and constraining the reactive gas in the chamber near the substrate tape, and the ex situ heat treatment of seed layer after deposition.

Prior Art

Best reported Jc results for HTS YBCO conductors have utilized a reactive electron beam evaporation technique to deposit CeO2 or Y2O3 films for seed layers (initial layer on the metal tape substrate). These reactive depositions typically require very high substrate temperatures in the range of 400°C to 700°C. Also, best results require a partial pressure of H2O. Typically tapes are heated with IR heaters, heated drums, and/or plates. H2O is leaked into the entire system through a variable leak valve. The initial layers of epitaxial film growth are typically deposited at lower deposition temperatures during a continuous process to prevent off texture. Higher deposition temperatures can lead to mixed or polycrystalline films due to Ni oxide growth.

Disadvantages of Prior Art

The disadvantages of the prior are as follows. Heating tapes is typically accomplished with IR heaters or heated drums or plates. The IR heater approach is difficult and very inefficient because of the poor thermal contact and reflectivity of the tape surface. This therefore results in the necessity for very high wattage heaters. Also, parts of the chamber are heated to significant temperatures using this approach. When parts of the chamber are heated to high temperatures they tend to outgas during the deposition and these species can be incorporated into the film. Another disadvantage of this approach is the life cycle of the heating elements which is short and the elements can fail during long runs. Heated drums and plates are also very inefficient since the entire drum or plate surface must be heated. Heat losses occur requiring significant power levels. Outgassing of the drum surface as well as the internal heating elements occur with this approach. Since this is a contact method, drum surfaces m...